Substrate with photocatalytic coating

ABSTRACT

The invention concerns a method from cathode spray deposition of a coating with photocatalytic properties comprising titanium oxide at least partly crystallised in anastatic form on a transparent or semi-transparent support substrate, such as glass, vitroceramic, plastic. The substrate is sprayed under a pressure of at least 2 Pa. The invention also concerns the resulting coated substrate, wherein said substrate constitutes the top layer of a series of thin antiglare layers.

[0001] The invention relates to generally transparent orsemi-transparent substrates, especially made of glass, plastic orglass-ceramic, and provided with a coating having photocatalyticproperties in order to endow them with an antistaining function or, moreexactly, a self-cleaning function.

[0002] An important application of these substrates relates to glazing,which may be in very varied applications, such as utilitarian glazing,glazing used in domestic electrical appliances, windows for vehicles,and windows for buildings.

[0003] It also applies to reflective glazing of the mirror type (mirrorsfor dwellings or rear-view mirrors for vehicles) and to opacifiedglazing of the apron wall or curtain walling type.

[0004] The invention also applies, similarly, to nontransparentsubstrates, such as ceramic substrates or any other substrate able inparticular to be used as an architectural material (metal, tiling,etc.). It preferably applies, whatever the nature of the substrate, tosubstantially plane or slightly curved substrates.

[0005] Photocatalytic coatings have already been studied, especiallythose based on titanium oxide crystallized in the anatase form. Theirability to degrade stains of organic origin or microorganisms under theaction of UV radiation is greatly beneficial. They also often have ahydrophilic nature, which allows the removal of inorganic stains by thespraying of water or, in the case of exterior windows, by rain.

[0006] This type of coating with antistaining, bactericidal andalgicidal properties has already been described, especially in patent Wo97/10186, which describes several methods of obtaining them.

[0007] The aim of the invention is therefore to improve the techniquesfor depositing this type of coating, especially for the purpose ofsimplifying them. In parallel, the aim of the invention is also toimprove the appearance of the coating, more particularly to improve theoptical properties of the substrate which is provided therewith.

[0008] The subject of the invention is firstly a process for depositinga coating having photocatalytic properties by sputtering, said coatingcomprising titanium oxide at least partly crystallized in the anataseform on a transparent or semitransparent carrier substrate. The featureof the invention consists in carrying out the sputtering on thesubstrate at a deposition pressure of at least 2 pascals. It ispreferably at most 6.67 Pa and especially at least 2.67 Pa (that is tosay at least 15 millitorr, especially between 20 and 50 millitorr).

[0009] In point of fact, as is known from the aforementioned patent WO97/10186, this type of coating can be deposited by sputtering. This is avacuum technique which in particular allows the thicknesses and thestoichiometry of the deposited layers to be very finely adjusted. It isgenerally enhanced by a magnetic field for greater efficiency. It may bereactive: in this case, an essentially metallic target is used, here atarget based on titanium (possibly alloyed with another metal or withsilicon), and the sputtering is carried out in an oxidizing atmosphere,generally an Ar/O₂ mixture. It may also be nonreactive: in this case atarget called a ceramic target is used, which is already in the oxidizedform of titanium (possibly alloyed).

[0010] However, the layers obtained by this type of technique aregenerally amorphous, whereas the functionality of the coating accordingto the invention is directly tied to the fact that it must besignificantly crystalline. This is the reason why, as is recommended inthe aforementioned patent, it is necessary to crystallize (or increasethe degree of crystallization) of the coating by making it undergo aheat treatment, for example from about 30 minutes to several hours at atleast 400° C.

[0011] According to the invention, it has been shown that a pressure ashigh as this favors particular crystallization of the layer and adensity/roughness level which have a significant impact on the level ofphotocatalytic properties of the coating. In some cases, the annealingmay become optional. To be specific, the deposition pressures generallyused for metal oxides are usually within the 2 to 8 millitorr (i.e. 0.27to 1.07 Pa) range: the invention therefore uses deposition pressureswhich are very unusual in this field.

[0012] It has also been shown within the context of the presentinvention that the post-deposition treatment step could possibly beeliminated, or at the very least made optional (and/or limited in termsof time or temperature), by sputtering the layer, not at ambienttemperature, but on a hot substrate, especially heating to at least 100°C. This heating during deposition is alternative or cumulative with theabovementioned use of high pressures.

[0013] This heating has at least five advantages:

[0014] a power saving during manufacture;

[0015] the possibility of using substrates which would be unable towithstand heat treatments at temperatures of 400 or 500° C., at leastwithout degradation;

[0016] if the annealing requires the interposition between substrate andphotocatalytic coating of a barrier layer preventing the diffusion ofelements from the substrate (of the alkali metal type when it is made ofglass), the possibility of using a thinner barrier layer, or even ofcompletely dispensing with the barrier layer, since the heat treatmentaccording to the invention is much less aggressive than an annealingoperation;

[0017] a much shorter manufacturing cycle (since the heat treatment ofthe substrate is substantially shortened and carried out at asubstantially lower temperature);

[0018] the need to store “semifinished” products to be annealed iseliminated.

[0019] However, levels of photocatalytic activity in the coatings verysimilar to those of coatings which are deposited and then annealed areobtained.

[0020] However, this was not a foregone conclusion, insofar as one mighthave expected that a prolonged annealing operation would beindispensable for making the crystalline seeds grow within the amorphousoxide matrix. This has not been the case: hot deposition favors directdeposition of an at least partly crystallized layer.

[0021] Nor was it obvious that the coating thus deposited “hot” wouldpreferentially crystallize in the anatase form rather than in the rutileform (the anatase form is much more photocatalytic than the rutile orbroockite form of titanium oxide).

[0022] There are various alternative ways of implementing the invention,especially depending on the type of sputtering apparatus available.Thus, it is possible to heat the substrate prior to the actualdeposition, outside the vacuum chamber. It is also possible to heat thesubstrate during deposition, when the deposition chamber is fitted withad hoc heating means. The substrate may therefore be heated before thecoating is sputtered and/or while it is being sputtered. The heating mayalso be gradual during deposition, or may affect only part of thethickness of the deposited layer (for example the upper part).

[0023] Advantageously, while the layer is being sputtered, the substrateis at a temperature between 150 and 350° C., preferably at least 200° C.and especially between 210 and 280° C. Surprisingly, it has thereforebeen possible to obtain sufficiently crystallized layers without havingto heat the substrate up to the temperatures generally used to carry outannealing operations, namely at least 400° C. to 500° C.

[0024] In general, when the coating is essentially based on titaniumoxide (TiO₂), and when it is deposited by sputtering (“hot” or atambient temperature), it has quite a high refractive index—greater than2 or than 2.1 or than 2.15 or 2.2. It is generally between 2.15 and 2.35or between 2.35 and 2.50 (it may be slightly substoichiometric),especially between 2.40 and 2.45. This is a feature quite specific tothis type of deposition, since coatings of the same type deposited byother techniques, for example by the sol-gel technique, tend to be muchmore porous and have significantly lower refractive indices (below 2 andeven below 1.8 or 1.7). The invention makes it possible to obtain layersby sputtering which have a porosity and/or a roughness (especially anRMS roughness), of between 2.5 and 10 nm, enhancing its photocatalyticproperties. Consequently, they may have refractive indices of about 2.15or 2.35, less than those usually obtained by sputtering—indirect proofof their porosity. This is an asset from the optical standpoint, sincelayers with a lower refractive index have a less reflective appearancefor a given thickness.

[0025] It has been observed that the crystallographic structure of thecoatings is influenced by the fact that they are deposited cold and thenannealed, or deposited hot. Thus, quite unexpectedly, the coatingsdeposited “hot” and/or at high pressure, in accordance with theinvention, generally have a TiO₂ mean crystallite size generally lessthan or equal to 50 or 40 or 30 nm, especially between 15 and 30 nm orbetween 20 and 40 nm. Coatings deposited in a standard manner,especially “cold” and then annealed, tend to comprise crystallites oflarger size, namely at least 30 or 40 nm and generally between 40 and 50nm, when standard deposition pressures are used.

[0026] On the other hand, if, according to one variant of the invention,the coating is deposited at ambient temperature but at high pressure,and then an annealing operation is carried out, the size of thecrystallites is of smaller size (20-40 nm), comparable to that of thecrystallites of coatings deposited hot, whether at high pressure or lowpressure.

[0027] The photocatalytic activity of coatings deposited at ambienttemperature and at high pressure, and then annealed, is much better thanthat of coatings deposited at ambient temperature and at low pressure,and then annealed: all other things being equal, it is clear that thedeposition pressure has a pronounced influence on the performance of thecoating, most particularly in the case of “cold” deposition.

[0028] Heating simultaneously with the growth of the layer results inthe formation of a microstructure conducive to a roughness and/orporosity favorable to the photocatalytic property. This is somewhat thesame as when a high deposition pressure is used (with “cold” depositionfollowed by an annealing operation, for example).

[0029] Thanks to the process according to the invention (by hot and/orhigh-pressure deposition), it is possible to obtain coatings having anPMS (root mean square) roughness measured by atomic force microscopy,taking measurements over the same surface with a pitch of 2 micrometers:

[0030] of at least 2 nm, especially at least 2.5 nm and preferablybetween 2.8 nm and 4.6 nm in the case of deposition at ambienttemperature and at high pressure within the meaning of the invention (2to 5 Pa), followed by annealing operations;

[0031] of at least 4 nm, especially at least 5 nm and preferably between5.5 and 6.0 nm in the case of hot deposition (at about 250° C.) withoutannealing, whether at high pressure or low pressure.

[0032] By way of comparison, the roughness of the coatings deposited atambient temperature and at standard pressure (especially 2×10-3millibars, i.e. 0.2 Pa) and then annealed is only 2 nm at best: thisproves that the use of high pressures makes it possible to achievesurprisingly high roughnesses for layers deposited by sputtering, thisconsequently improving the photocatalytic properties of the coating.

[0033] Advantageously, the coating has a geometrical thickness of lessthan 150 nm, especially between 80 and 120 nm or between 10 and 25 nm.It turns out that the coating, even when very thin, can havesufficiently photocatalytic properties (at least for some applications)with, in addition, the optical advantage of being hardly reflective.

[0034] As will have been seen above, the sputtering of the coating maybe reactive or nonreactive. In either case, the target to be sputteredmay be doped, especially with at least one metal. This may be one ormore metals chosen from the following list: Nb, Ta, Fe, Bi, Co, Ni, Cu,Ru, Ce, Mo, Al.

[0035] The deposition process according to the invention may be precededand/or followed by one or more steps of depositing one or more otherthin layers, especially with an optical, antistatic, anticolor,antireflective, hydrophilic or protective function, or to increase theroughness of the coating having photocatalytic properties. Thus, it hasbeen observed that there may be advantage in depositing one layer (atleast) so that it is particularly rough, for example by pyrolysis or bysol-gel, and then the photocatalytic coating; the coating then tends to“follow” the roughness of the underlayer and in fact to have, it too, asignificant roughness, whereas layers deposited by sputtering haveinstead a tendency to be not very rough. Thus, it is possible to formmultilayers with a sublayer (having an RMS roughness of, for example, atleast 5 or 10 nm) of the SiO₂, SiOC or SiON type, deposited by chemicalvapor deposition (CVD), and then the photocatalytic layer by sputtering.

[0036] The invention therefore comprises any combination of depositionof one or more layers by sputtering (including at least thephotocatalytic coating) and deposition of the other layer(s) of themultilayer by a technique involving thermal decomposition, especiallypyrolysis (in liquid, vapor or pulverulant phase), or a sol-geltechnique.

[0037] As was seen above, photocatalytic TiO₂-based coatings have a highrefractive index. This means that they are reflective and endow theircarrier substrate with a reflective appearance often regarded as notbeing very esthetically attractive. Apart from this shiny character, thecolor in reflection may also be undesirable. It is not simple to improvethis appearance in reflection, since the photocatalytic functionalityimposes constraints—the coating must in general be in contact with theexternal atmosphere in order to receive UV radiation and degrade theexternal stains. It therefore cannot be covered with a low-index layer(unless this is very thin and/or porous). It must also have a specificminimum thickness in order to be sufficiently effective.

[0038] Another part of the present invention has therefore consisted inimproving the appearance of the substrate in reflection, withoutdisturbing the photocatalytic activity of the coating, especially bylowering its light reflection as much as possible and/or by giving it acolor in reflection which is as neutral as possible.

[0039] The subject of the invention is therefore also the transparent orsemitransparent substrate defined above, provided over at least part ofat least one of its faces with a photocatalytic coating comprisingtitanium oxide at least partly crystallized as anatase, this coatinghaving a high refractive index, of at least 2 or 2.1 or 2.2. Accordingto the invention, this coating is regarded as forming part of amultilayer consisting of thin antireflection layers, the coating beingthe final layer (that is to say the layer furthest from the carriersubstrate). The antireflection multilayer is composed of an alternationof high-index and low-index layers and is therefore completed in thepresent case with the layer having a high photocatalytic index. Thisterm “antireflection” is used for convenience: in general, it isemployed when it is desired to obtain a light reflection less than thatwhich the substrate alone would have. Within the context of theinvention, it is more a question of limiting the increase in lightreflection (and/or modifying or attenuating its color in reflection)caused by the use of a coating containing titanium oxide.

[0040] Within the context of the invention, the term “layer” isunderstood to mean a single layer or a superposition of layers. If it isa superposition of layers, its overall thickness is regarded as the sumof the thicknesses of each of the layers and its overall index isregarded as the average of all of the refractive indices of said layers.This also applies to the photocatalytic coating. It may also beassociated with another high-index layer.

[0041] Within the context of the invention and as recalled above, theterm “antireflection” is understood to mean the function which makes itpossible to lower the light reflection value of the coated substrateand/or to attenuate its color in reflection, especially so as to make itas pale and as neutral as possible, i.e. as esthetically attractive aspossible (in this case one also speaks of an “anticolor” effect).

[0042] This is a quite free and unexpected adaptation of conventionalantireflection multilayers. This is because, in a known manner, thesemultilayers alternate high-index and low-index layers and are completedwith low-index layers (the index being as close as possible to therefractive index of air, equal to 1) and are generally layers based onSiO₂, MgF₂, etc. However, in the present case, the multilayer iscompleted with a high-index layer, something which is quite paradoxical.Nevertheless, by appropriately selecting the characteristics of thevarious layers, this particular antireflection multilayer is able tosignificantly attenuate the reflective nature intrinsic to high-indexTiO₂ and to give the substrate an acceptable color in reflection(neutral, in pale tints avoiding reds and other hot colors, deemed notvery esthetically attractive, in favor of gray, blue or especiallygreen).

[0043] Advantageously, the photocatalytic coating has a refractive indexgreater than or equal to 2.30, especially between 2.35 and 2.50, orbetween 2.40 and 2.45 (as seen above, it is also possible to deposit itso that it has an index of only 2.10 to 2.30). It is preferablydeposited by sputtering. Its optical thickness, in conjunction with thethicknesses of the other layers of the multilayer, is advantageouslyselected so as to reduce the light reflection of the substrate. It hasbeen shown that the optimum optical thickness is preferably in theregion of λ/2, where λis about 580 nm. This corresponds to an opticalthickness of between 250 and 350 nm, especially between 270 and 310 nm,and to a geometrical thickness of between 80 and 120 nm, especiallybetween 90 and 110 nm. This geometrical thickness range has provedsufficient to obtain, in parallel, a photocatalytic activity regarded assufficient (the photocatalytic activity depends in fact on numerousparameters, including the thickness but also the surface roughness, thecrystalline morphology of the layer, its porosity, etc.). It is alsopossible to use substantially thinner layers, having in particular ageometrical thickness between 10 and 25 nm.

[0044] Depending on whether the coating is deposited by “hot” sputteringor sputtering at cold ambient temperature and annealing, it containscrystallites varying in size as was seen above (generally less than 30nm when sputtered “hot” and about 30 to 50 nm or more when sputtered atambient temperature and at standard pressure, as seen above).

[0045] The antireflection multilayer of the invention, in its simplestembodiment, comprises three layers, these being, in succession, ahigh-index layer, a low-index layer and then the high-indexphotocatalytic coating.

[0046] The high-index layer(s) of the multilayer, apart from thephotocatalytic coating, has (have) in general an index of at least 1.9,especially between 1.9 and 2.3 or between 1.9 and 2.2. Said layer(s) maybe made of zinc oxide, tin oxide, zirconium oxide, aluminum nitride orsilicon nitride. It (they) may also be made of a mixture of at least twoof these compounds.

[0047] The optical thickness of these high-index layers is selected.Their optimum optical thickness is preferably in the region of λ/10,where λ is about 580 nm. This corresponds to an optical thickness ofbetween 48 and 68 nm, especially between 53 and 63 nm, and to ageometrical thickness of between 20 and 40 nm, especially between 25 and35 nm. It is also possible to choose a smaller thickness, especiallybetween 20 and 48 nm.

[0048] The low-index layer(s) has (have) in general an index of between1.4 and 1.75, especially between 1.45 and 1.65. They may, for example,be based on silicon oxide, aluminum oxide or a mixture of the two. Theoptical thickness of these low-index layers is selected: their optimumoptical thickness is preferably in the region of λ/20, where λ is about580 nm. This corresponds to an optical thickness of between 20 and 79nm, especially between 19 and 39 nm, especially between 25 and 35 nm,and to a geometrical thickness of between 12 and 50 nm, especiallybetween 15 and 30 nm, for example between 20 and 28 nm.

[0049] According to another variant, in the abovementioned three-layermultilayer, it is possible to replace the high-index layer/low-indexlayer sequence with a layer having an “intermediate” refractive index,that is to say one preferably greater than 1.65 and less than 1.9. Thepreferred range of indices is between 1.75 and 1.85. It may be based onsilicon oxynitride and/or aluminum oxynitride. It may also be based on amixture of a low-index oxide such as SiO₂ and at least one oxide ofhigher index, such as SnO₂, ZnO, ZrO₂, TiO₂ (the relative proportionbetween the oxides allows the index to be adjusted).

[0050] It is also possible to use this intermediate layer to replace thefirst sequence—high-index layer/low-index layer—with a multilayercontaining not three but five or seven layers for example.

[0051] The optical thickness of this intermediate-index layer isselected. The optimum optical thickness is in the region of λ/4, where λis about 580 nm. This corresponds to an optical thickness of between 120and 150 nm, especially between 125 and 135 nm, and to a geometricalthickness of between 65 and 80 nm, especially between 68 and 76 nm.

[0052] As mentioned above, these various optical thickness selectionstake into account the overall appearance of the substrate in reflection:endeavors are made not only to lower the light reflection value RL butalso to give it a tint which today is deemed to be estheticallyattractive (that is to say rather in cold colors than toward yellow orred) and has the lowest possible intensity. It is therefore necessary tofind the best compromise so that, overall, the appearance of thesubstrate in reflection is better. Depending on the applications,preference may be given more to lowering the value of R1 [sic] or moreto selecting a particular calorimetric response in reflection (forexample quantified by the a* and b* values of the L,a*,b* colorimetrysystem or by the value of the dominant wavelength associated with thecolor purity).

[0053] Advantageously, all of the layers of the antireflectionmultilayer may be deposited by sputtering, one after the other, on thesame production line.

[0054] According to an optional variant of the invention, it is possibleto insert, between the substrate and the antireflection multilayer, abarrier layer blocking the species liable to diffuse out of thesubstrate. These are, in particular, alkali metals when the substrate ismade of glass. For example, the barrier layer is based on silicon oxide(or oxycarbide): SiO₂ may be deposited by sputtering and SiOC, in aknown manner, by chemical vapor deposition (CVD). It preferably has athickness of at least 50 nm, for example between 80 and 200 nm. Whenchosen in this type of material, having a relatively low index (around1.45 to 1.55), it is in fact, generally, pretty much “neutral” from theoptical standpoint. Silicon oxide may contain minority elements,especially chosen from Al, C, N.

[0055] The subject of the invention is also glazing, especiallysingle-glazing (a rigid substrate), laminated glazing and multipleglazing of the double-glazing type, which comprises at least onesubstrate coated in the manner described above.

[0056] Said glazing preferably has, thanks to the antireflection effectof the invention, a light reflection R_(L) (on the multilayer side)which remains at most 20%, especially at most 18%. Preferably, thislight reflection has a pleasant tint in the blues or greens, withnegative a* and b* values in the (L,a*,b*) colorimetry system andespecially less than 3 or 2.5 in absolute values. The tint is thus acolor both pleasing to the eye and pale, of low intensity.

[0057] The glazing may also include one or more other functionalcoatings (deposited by sputtering or pyrolysis or sol-gel), either onthe same face of the substrate provided with the photocatalytic coating,or on the opposite face of this substrate, or on a face of anothersubstrate associated with the first in a glazing unit (double glazing orlaminated glazing). It is also possible to have a double-glazing unit ofthe glass/gas-filled cavity/glass type with, on the exterior face(s) ofthe glass pane(s), the photocatalytic coating and, on the internal faces(turned toward the gas-filled cavity), a multilayer containing one ortwo silver layers. The same type of configuration applies to laminatedglazing.

[0058] The other functional coating(s) may in particular be anantistaining, solar-protection, low-emissivity, heating, hydrophobic,hydrophilic, antireflection or antistatic coating or anotherphotocatalytic coating, etc. Mention may especially be made ofsolar-protection or low-emissivity multilayers consisting of one or morelayers of silver, or nickel-chromium, or titanium nitride or zirconiumnitride. In the case of layers based on a metal nitride, it is possibleto use a CVD technique.

[0059] The invention will now be described in greater detail, withnonlimiting illustrative examples.

[0060] Example 1 and Comparative Example 1 relate to the hot depositionof photocatalytic TiO₂ layers by sputtering.

EXAMPLE 1

[0061] The following were deposited on a clear silica-soda-lime glass 4mm in thickness: an 80-nm SiOC first layer by CVD and then a 90-nmphotocatalytic TiO₂ second layer (it is also possible to substitute theSiOC layer with an Al:SiO₂ layer obtained by reactive sputtering from anAl-doped Si target).

[0062] The TiO₂ layer was deposited by magnetic-field-enhancedsputtering. This is reactive sputtering, in the presence of oxygen, froma titanium target. The glass was preheated to a temperature of about220° C. to 250° C. This temperature was kept constant to within 5° C.during sputtering of the layer, using a heater placed opposite thetarget.

[0063] The TiO₂ layer obtained had a refractive index of 2.44. Itcrystallized in the anatase form (it may also include amorphousregions), with an average crystallite size of less than 25 nm.

[0064] Its photocatalytic activity was quantified by means of a testusing palmitic acid: this consists in depositing a given thickness ofpalmitic acid on a photocatalytic coating, in exposing the latter to UVradiation centered on 365 nm with a surface power density of about 50W/m² throughout the entire duration of the test, and then in measuringthe rate of disappearance of the palmitic acid according to thefollowing equation:${V\quad \left( {{nm}\text{/}h} \right)} = \frac{\left\lbrack {{palmitic}\quad {acid}\quad {thickness}\quad ({nm})} \right\rbrack}{\left\lbrack {2\quad t_{{1/2}\quad {disappearance}}\quad (h)} \right\rbrack}$

[0065] With the layer according to the invention, a photocatalyticactivity of at least 10 nm/h, especially at least 20 nm/h, especiallybetween 20 and 100 nm/h, depending on the choice of the depositionparameters of the pressure and temperature type, was obtained using thiscalculation.

[0066] The glass thus coated with the two layers had, under illuminantD₆₅, a light reflection R_(L) of 23%, with a* and b* values inreflection in the (L,a*,b*) colorimetry system of about 17 and 28,respectively.

[0067] The photocatalytic activity of the layer is therefore useful, butits optical appearance is still clearly reflective, with too intense acolor.

[0068] It should be noted that it is possible to increase thephotocatalytic activity of the layer by subjecting it, after deposition,to a conventional annealing operation (for one or several hours at atleast 400° C.).

COMPARATIVE EXAMPLE 1

[0069] Example 1 was repeated, but this time the TiO₂ layer wasdeposited on an unheated substrate and then treated for four hours atabout 500 to 550° C. Furthermore, the SiO₂ sublayer was thickened to 100nm. The morphology of the layer was a little different, having a meancrystallite size somewhat greater than 30 nm.

[0070] Its photocatalytic activity was similar to that of the unannealedlayer of Example 1, but it was less than it if a smaller thickness ofSiO₂ sublayer was chosen.

[0071] This therefore confirms that the “hot” deposition according tothe invention, making it possible to “save” on an often lengthyannealing operation, is not obtained to the detriment of the performanceof the layer. This also confirms a subsidiary advantage of theinvention: by depositing hot and dispensing with an annealing operation,it is possible to use, for identical photocatalytic performance, athinner barrier sublayer (hence, again, resulting in a reduced productmanufacturing cost).

[0072] Example 2 and the following examples relate to the incorporationof a photocatalytic layer of high-index TiO₂, said layer beingespecially deposited by sputtering, into antireflection multilayers inorder to improve the optical properties thereof.

EXAMPLE 2 (REALIZED)

[0073] The following multilayer stack was deposited on asilica-soda-lime float glass 4 mm in thickness: glass/Si₃N₄ ⁽¹⁾/SiO₂⁽²⁾/TiO₂ ⁽³⁾ 30 nm 22 nm 104 nm (geometrical thicknesses).

[0074] The Si₃N₄ layer (1) was deposited by reactive sputtering in thepresence of nitrogen from an Al-doped Si target.

[0075] The SiO₂ layer (2) was deposited by reactive sputtering in thepresence of oxygen from an Al-doped Si target.

[0076] The photocatalytic TiO₂ layer (3) was deposited hot, as describedin Example 1.

[0077] Optionally, it is possible to insert an additional layer, betweenthe glass and the Si₃N₄ layer, [lacuna] a layer of SiO₂ of about 100 nmobtained, like the other SiO₂ layer (2) described above. It hasvirtually no influence on the optical properties of the substrate andmay serve as an alkali-metal barrier layer to the glass. This isoptional, all the more so since the layers of the antireflection coatingbeneath the photocatalytic layer, namely the layers (1) and (2),themselves constitute very satisfactory barrier layers, in addition totheir optical properties: these two layers already form a 100-nm barrierto the species liable to diffuse out of the glass.

[0078] The photocatalytic activity of the layer 3 was 80 nm/h.

[0079] Alternatively, a TiO₂ layer deposited cold and then annealed, asdescribed in Comparative Example 1, could have been used.

[0080] The results for such a multilayer, in reflection on themultilayer side, were the following: R_(L) (under illuminant D₆₅) =17.3% a* (R_(L)) = −2 b* (R_(L)) = −2.8 λ_(d) (dominant wavelength ofthe light 494 nm reflection) = ρe (purity of the color in 2.5%.reflection) =

[0081] This shows, compared with Example 1, a significant reduction inthe value of R_(L) and in this case a paler color in the blue-greens isobtained. Overall, the appearance in reflection is thereforeesthetically and substantially improved.

EXAMPLE 3

[0082] This is very similar to Example 2, the only change being a slightreduction in the thickness of the TiO₂ layer.

[0083] Here, the following were deposited: glass/Si₃N₄ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂⁽³⁾ 30 nm 22 nm 99 nm (geometrical thicknesses).

[0084] The results in light reflection were the following (with the sameconventions as for Example 2): R_(L) = 17.9% a* = −0.8 b* = −0.7 λ_(d) =494 nm ρe = 0.8%.

[0085] In this case, therefore, there is a slightly differentcompromise, with a slightly greater R_(L) value but a* and b* valueslower in terms of absolute values.

EXAMPLE 4 (Modeling)

[0086] This is very similar to Example 2, the only change being thethickness of the Si₃N₄ first layer: glass/Si₃N₄ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂ ⁽³⁾ 22nm 104 nm (geometrical thicknesses).

[0087] The results in light reflection were the following (again withthe same conventions):

[0088] In this case, the value of R_(L) was greatly lowered, but thecolor in reflection changed tint.

EXAMPLE 5 (Modeling/Comparative)

[0089] Here, compared with Example 2, all the thicknesses have changed.

[0090] We have: glass/Si₃N₄ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂ ⁽³⁾ 28 nm 30 nm 75 nm(geometrical thicknesses).

[0091] The results in light reflection were the following R_(L) = 25.8%a* = −0.3 b* = −0.7 λ_(d) = 492 nm ρe = 0.5%.

[0092] Although the substrate has a satisfactory color in reflection, itdoes have, however, an RL value well above 20%, which is too high: thechosen thicknesses are not optimal.

EXAMPLE 6 (Modeling/Comparative)

[0093] This example departs even further from the layer thicknessesrecommended by the invention, with the following multilayer: glass/Si₃N₄⁽¹⁾/SiO₂ ⁽²⁾/TiO₂ ⁽³⁾ 20 nm 20 nm 60 nm (geometrical thicknesses).

[0094] The results in light reflection were the following: R_(L) = 30%a* = 2.3 b* = 7.2 λ_(d) = 587 nm ρe = 14%.

[0095] The multilayer has both a very high R_(L) value and a not verydesirable and more intense color in reflection. Its appearance inreflection is therefore unsatisfactory.

EXAMPLE 7 (Realized)

[0096] The stack this time was as follows: glass/SnO₂ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂⁽³⁾ 30 nm 27 nm 105 nm (geometrical thicknesses).

[0097] Si₃N₄ has therefore been replaced with SnO₂, deposited byreactive sputtering in the presence of oxygen from a tin target.

[0098] The results in light reflection were the following: R_(L) = 17.4%a* = −2.8 b* = −2.7 λ_(d) = 496 nm ρe = 2.8%.

[0099] The appearance in reflection is similar to that obtained inExample 2.

EXAMPLE 8 (Modeled)

[0100] Here, the first two layers were replaced with a single layer ofsilicon oxynitride SiON with an index of 1.84.

[0101] The multilayer was therefore the following: glass/SiON/TiO₂ 72 nm101 nm (geometrical thicknesses).

[0102] The results in light reflection were the following: R_(L) = 17.4%a* = 0 b* = −1.08 λ_(d) = 480 nm ρe = 1%.

[0103] The appearance in reflection is therefore satisfactory.

EXAMPLE 9 (Modeled)

[0104] This repeats Example 8, but with a 1.86 index for the SiON layer.

[0105] The appearance in reflection is slightly modified therefrom:R_(L) = 17.8% a* = −1.1 b* = −1.5 λ_(d) = 494 nm ρe = 1.3%.

EXAMPLE 10 (Realized)

[0106] The multilayer was the following: glass/Si₃N₄ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂⁽³⁾/TiO₂ ⁽³⁾ 24 nm 17.5 nm 24 nm 92.5 nm

[0107] The final high-index “layer” was therefore the superposition ofan Si₃N₄ layer and a TiO₂ layer. The light reflection R_(L) on themultilayer side was between 16.5 and 17.5%, and the photocatalyticactivity was in the region of 80 nm/h.

EXAMPLE 11 (Realized)

[0108] The type of multilayer in Example 3 was repeated, but withdifferent thicknesses. The multilayer was: glass/Si₃N₄ ⁽¹⁾/SiO₂ ⁽²⁾/TiO₂⁽³⁾ 14.5 nm 43 nm 14.5 nm

[0109] The light reflection on the multilayer side was between 13 and16%. If each of the layers of the stack were varied by 3%, the opticalvariations in the substrate thus coated were the following: ΔR_(L): 0.8%Δa* (R_(L)): 0.3  Δb* (R_(L)): 1.3.

[0110] This example shows a photocatalytic activity of about 15 to 20nm/h.

[0111] This example is useful on several counts: it is very insensitiveto variations in thickness and will therefore be easy to produce on anindustrial scale. It remains sufficiently photocatalytic, even thoughthe titanium oxide layer is very thin. It is satisfactory from thecalorimetric standpoint.

[0112] In conclusion, the invention has developed a novel way ofvacuum-depositing layers containing photocatalytic TiO₂. It has alsodeveloped a novel type of antireflection/anticolor multilayer which iscompleted with a high-index layer, said multilayer being simple toproduce on an industrial scale and significantly attenuating thereflective aspect of TiO₂ without degrading the photocatalyticproperties thereof. It makes it possible to obtain glazing in the bluesor in the pale greens in reflection, while maintaining consistentphotocatalytic layer thicknesses of the order of one hundred nanometers.It is also possible to choose a substantially thinner, 12-30 nm,photocatalytic layer.

[0113] The invention in its two aspects (product and process) may applyin the same way to photocatalytic coatings which do not contain TiO₂.

[0114] The invention therefore proposes that these coatings be deposited“hot” and, alternatively, deposited at ambient temperature, followed byappropriate heat treatments, preferably with the deposition pressurebeing particularly controlled, in order to obtain vacuum-depositedlayers having very unusual characteristics, resulting in remarkableantistaining properties.

1. A process for depositing a coating having photocatalytic propertiesby sputtering, said coating comprising titanium oxide at least partlycrystallized, especially in the anatase form on a transparent orsemitransparent carrier substrate of the glass, glass-ceramic or plastictype, characterized in that the sputtering is carried out at adeposition pressure P of at least 2 Pa.
 2. The deposition process asclaimed in claim 1, characterized in that the deposition pressure P isat most 6.67 Pa and especially at least 2.67 Pa.
 3. The depositionprocess as claimed in either of the preceding claims, characterized inthat the sputtering is carried out on the substrate heated to atemperature of at least 100° C.
 4. The process as claimed in claim 3,characterized in that the substrate is heated before and/or during thesputtering and/or during at least part of the sputtering.
 5. The processas claimed in claim 3 or claim 4, characterized in that, during thesputtering, the substrate is at a temperature between 150 and 350° C.,preferably at a temperature of at least 200° C. and especially between210 and 280° C.
 6. The deposition process as claimed in claim 1 or claim2, characterized in that the sputtering is carried out ambienttemperature, the deposition of the coating being optionally followed bya heat treatment of the annealing type.
 7. The process as claimed in oneof the preceding claims, characterized in that the coating has arefractive index greater than 2, especially greater than 2.1, preferablybetween 2.15 and 2.35 or between 2.35 and 2.50.
 8. The process asclaimed in one of the preceding claims, characterized in that thecoating contains titanium oxide crystallites having a size of less thanor equal to 50 or 40 nm, preferably between 15 and 30 nm or between 20and 40 nm.
 9. The deposition process as claimed in one of the precedingclaims, characterized in that the coating has an RMS roughness of atleast 2 nm, especially at most 10 nm, preferably between 2.5 and 7 nm orbetween 2.8 and 5 nm.
 10. The deposition process as claimed in one ofthe preceding claims, characterized in that the coating has ageometrical thickness of less than 150 nm, especially between 80 and 120nm or between 10 and 25 nm.
 11. The deposition process as claimed in oneof the preceding claims, characterized in that the sputtering is carriedout in a reactive manner from an essentially metallic target, or in anonreactive manner from a ceramic target.
 12. The deposition process asclaimed in claim 11, characterized in that the target to be sputtered isdoped with a metal, especially one chosen from Nb, Ta, Fe, Bi, Co, Ni,Cu, Ru, Ce, Mo, Al.
 13. The deposition process as claimed in one of thepreceding claims, characterized in that it is preceded and/or followedby a step of depositing at least one thin layer, especially with anoptical, antistatic, anticolor, antireflective, hydrophilic orprotective function, or to increase the roughness of the coating havingphotocatalytic properties, by a sputtering technique or by a techniqueinvolving thermal decomposition of the pyrolysis type or by sol-gel. 14.The deposition process as claimed in claim 13, characterized in that itis preceded by the deposition of at least one thin layer by pyrolysis,especially by CVD, said thin layer having an RMS roughness of at least 5nm, especially at least 10 nm.
 15. A transparent or semitransparentsubstrate of the glass, glass-ceramic or plastic substrate [sic] type,provided over at least part of one of its faces with a coating havingphotocatalytic properties, comprising titanium oxide at least partiallycrystallized, especially in the anatase form, obtained in accordancewith one of the preceding claims.
 16. The transparent or semitransparentsubstrate, of the glass, glass-ceramic or plastic substrate [sic] type,provided over at least part of one of its faces with a coating havingphotocatalytic properties, comprising titanium oxide at least partiallycrystallized, especially in the anatase form, obtained by sputtering andhaving an RMS roughness of at least 2 nm, especially at least 2.5 to 2.8nm, and preferably at most 1 nm [sic].
 17. The transparent orsemitransparent substrate, of the glass, glass-ceramic or plasticsubstrate [sic] type, provided over at least part of at least one of itsfaces with a coating having photocatalytic properties, comprisingtitanium oxide at least partially crystallized, especially in theanatase form, characterized in that said coating has a high refractiveindex of at least 2, especially at least 2.1, and of at most 2.45 or2.35, and in that it constitutes the final layer of a multilayerconsisting of thin “antireflection” layers, said multilayer beingcomposed of an alternation of layers having high and low refractiveindices.
 18. The substrate as claimed in claim 17, characterized in thatthe coating having photocatalytic properties has a refractive index ofgreater than or equal to 2.30, especially between 2.35 and 2.50, or lessthan or equal to 2.30, especially between 2.15 and 2.25.
 19. Thesubstrate as claimed in claim 17 or claim 18, characterized in that thecoating having photocatalytic properties has an optical thickness ofbetween 200 and 350 nm, especially between 210 and 310 nm.
 20. Thesubstrate as claimed in claim 17 or 18, characterized in that thecoating having photocatalytic properties has an optical thickness ofless than 50 nm, especially between 25 and 45 nm.
 21. The substrate asclaimed in either of claims 17 and 18, characterized in that the coatinghaving photocatalytic properties has a geometrical thickness of between80 and 120 nm, preferably between 90 and 110 nm, or between 10 and 25nm.
 22. The substrate as claimed in one of claims 17 to 20,characterized in that the coating having photocatalytic properties isdeposited by sputtering in accordance with the process as claimed in oneof claims 1 to
 14. 23. The substrate as claimed in one of claims 17 to22, characterized in that the coating having photocatalytic propertiescontains titanium oxide crystallites having a size of less than or equalto 50 or 40 nm, especially between 15 and 30 nm or 20 to 40 nm, ortitanium oxide crystallites having a size of at least 30 nm, especiallybetween 30 and 50 nm.
 24. The substrate as claimed in one of claims 17to 23, characterized in that the antireflection multilayer comprises atleast three layers, namely, in succession, a first layer having a highrefractive index, a second layer having a low refractive index and thecoating having photocatalytic properties, which may or may not becombined with at least one other layer having a high refractive index.25. The substrate as claimed in one of claims 17 to 24, characterized inthat the high-index layer(s) has (have) an index of at least 1.9,especially between 1.9 and 2.3 or between 1.9 and 2.2, for example onebased on tin oxide, zinc oxide, zirconium oxide, aluminum nitride orsilicon nitride or based on a mixture of at least two of thesecompounds.
 26. The substrate as claimed in claim 24 or claim 25,characterized in that the high-index first layer has an opticalthickness of between 48 and 68 nm, especially between 53 and 63 nm orbetween 20 and 48 nm.
 27. The substrate as claimed in either of claims24 and 25, characterized in that the high-index first layer has ageometrical thickness of between 20 and 40 nm, or between 25 and 35 nm,or between 10 and 20 nm.
 28. The substrate as claimed in one of claims17 to 27, characterized in that the layer(s) having a low refractiveindex has (have) an index of between 1.40 and 1.75, especially between1.45 and 1.55, for example one based on silicon oxide, aluminum oxide ora mixture of the two.
 29. The substrate as claimed in one of claims 12to 17, characterized in that the layer having a low refractive index hasan optical thickness of between 20 and 79 nm.
 30. The substrate asclaimed in one of claims 17 to 29, characterized in that the layerhaving a low refractive index has a geometrical thickness of between 12and 50 nm, especially 15 and 30 nm.
 31. The substrate as claimed inclaim 24, characterized in that the high-index layer and the low-indexlayer are replaced with a layer having an intermediate refractive index,which is greater than 1.65 and less than 1.9, especially between 1.75and 1.85.
 32. The substrate as claimed in claim 31, characterized inthat the intermediate-index layer is based on silicon oxynitride and/oron aluminum oxynitride or based on a mixture of silicon oxide and atleast one other oxide, taken from tin oxide, zirconium oxide, titaniumoxide and zinc oxide.
 33. The substrate as claimed in claim 31 or claim32, characterized in that the intermediate-index layer has an opticalthickness of between 120 and 150 nm, especially between 125 and 135 nm,preferably with a geometrical thickness of between 65 and 80 nm,especially between 68 and 76 nm.
 34. The substrate as claimed in one ofclaims 17 to 33, characterized in that a barrier layer blocking thespecies liable to diffuse out of the substrate, of the alkali metaltype, is interposed between said substrate and the antireflectionmultilayer.
 35. The substrate as claimed in claim 34, characterized inthat the barrier layer is based on silicon oxide, possibly containingAl, C or N, especially with a thickness of at least 50 nm, for examplebetween 60 or 80 nm and 200 nm.
 36. Glazing, especially single glazing,laminated glazing or multiglazing of the double-glazing type,characterized in that it includes at least one substrate as claimed inone of claims 16 to
 34. 37. The glazing as claimed in claim 36,characterized in that it has a light reflection R_(L) on the multilayerside of at most 20%, especially at most 18%.
 38. The glazing as claimedin claim 36 or claim 37, characterized in that it has a lightreflection, on the multilayer side, in the blues or the greens, withnegative a* and b* values in the (L,a*,b*) colorimetry system which arepreferably less than 3 or 2.5 in absolute values.
 39. The glazing asclaimed in claim 36, characterized in that it also includes at least oneother functional coating, especially an antistaining, solar-protection,low-emissivity, heating, hydrophobic, hydrophilic, antireflection orantistatic coating, or a second coating having photocatalyticproperties.